During the investigation, there was no confirmed indication of any mechanical problem with the aircraft. The accuracy of a general reference to an unspecified problem with the tail of the aircraft, that had apparently occurred at sometime prior to the accident flight, was not determined; however, the departure from the St. Marys River and arrival at Buck Lake were normal and indicate the aircraft was operating correctly. The aircraft apparently left from Buck Lake and returned to the St. Marys River sometime in the late afternoon. The position of the throttle, carburettor heat and magneto controls is consistent with normal engine operation at reduced power, such as would be expected for a normal landing. The lack of any substantial damage to the aircraft, combined with the minor injuries to the occupants from any impact forces, indicated that the aircraft was stopped or travelling at a slow speed when it broke through the ice. The fact that the seat-belts were undone, that both cabin doors were open, and that both occupants were found outside of the aircraft indicates that they had sufficient time to exit the aircraft as it sank, or that they were not in the aircraft when it started to sink. With a water temperature of about one degree Celsius, the survival time in the water would have been very short. It would have been an extremely difficult task for both of the occupants to swim and get out of the water with the wet, heavy winter clothing they had on. There were no known mechanical problems with the aircraft or any medical conditions of the pilot that were considered to be contributory to the accident.Analysis During the investigation, there was no confirmed indication of any mechanical problem with the aircraft. The accuracy of a general reference to an unspecified problem with the tail of the aircraft, that had apparently occurred at sometime prior to the accident flight, was not determined; however, the departure from the St. Marys River and arrival at Buck Lake were normal and indicate the aircraft was operating correctly. The aircraft apparently left from Buck Lake and returned to the St. Marys River sometime in the late afternoon. The position of the throttle, carburettor heat and magneto controls is consistent with normal engine operation at reduced power, such as would be expected for a normal landing. The lack of any substantial damage to the aircraft, combined with the minor injuries to the occupants from any impact forces, indicated that the aircraft was stopped or travelling at a slow speed when it broke through the ice. The fact that the seat-belts were undone, that both cabin doors were open, and that both occupants were found outside of the aircraft indicates that they had sufficient time to exit the aircraft as it sank, or that they were not in the aircraft when it started to sink. With a water temperature of about one degree Celsius, the survival time in the water would have been very short. It would have been an extremely difficult task for both of the occupants to swim and get out of the water with the wet, heavy winter clothing they had on. There were no known mechanical problems with the aircraft or any medical conditions of the pilot that were considered to be contributory to the accident. During the landing roll at slow speed or just after coming to a stop, the aircraft broke through a thin layer of the ice which covered the St. Marys River. Both the pilot and passenger, if still in the aircraft as it sank, were able to exit the aircraft, but were unable to get out of the water. The pilot and the passenger succumbed to hypothermia and drowning. The pilot was properly qualified and licensed. There was no evidence that mechanical problems contributed to the accident. The search for the aircraft was hampered by darkness and the fact that the aircraft had sunk in the water.Findings During the landing roll at slow speed or just after coming to a stop, the aircraft broke through a thin layer of the ice which covered the St. Marys River. Both the pilot and passenger, if still in the aircraft as it sank, were able to exit the aircraft, but were unable to get out of the water. The pilot and the passenger succumbed to hypothermia and drowning. The pilot was properly qualified and licensed. There was no evidence that mechanical problems contributed to the accident. The search for the aircraft was hampered by darkness and the fact that the aircraft had sunk in the water. The Aeronca 11CC broke through a thin layer of ice on the St. Mary's river either at slow speed during, or stopped at the end of, the landing roll. Contributing to this fatal accident were the water temperature of one degree Celsius, and the winter clothing worn by the pilot and passenger which would have hampered their ability to swim and get out of the water.Causes and Contributing Factors The Aeronca 11CC broke through a thin layer of ice on the St. Mary's river either at slow speed during, or stopped at the end of, the landing roll. Contributing to this fatal accident were the water temperature of one degree Celsius, and the winter clothing worn by the pilot and passenger which would have hampered their ability to swim and get out of the water.